Collagen casings are widely used and have certain advantages over natural casings produced from sheep or hog intestines. Thus, collagen casings are of uniform diameter and strength and have a good finish. However, they do not look the same nor do they handle in the same way as natural casings. Some users prefer the appearance and feel of natural casings. However, because natural casings come in short lengths, processing costs are high, their mechanical strength may be unreliable and the use of natural casings is labour-intensive and costly.
Collagen casings are conventionally produced in the wet state and are subsequently dried prior to packaging. The dried casings have good mechanical properties in terms of tensile strength, burst strength, hoop strength and bite resistance. Whilst the conventional collagen casing in its wet state to some extent approximates natural casings, generally the mechanical properties are inadequate.
In one conventional process for producing collagen casings, acid collagen gel obtained from hide splits is extruded to form a continuous tube, hardened using ammonia and washed. The collagen gel may include a proportion of cellulose. The casing is partially dried by passing through a bath containing sodium carboxymethyl cellulose as a drying agent and glycerol as a humectant. The casing is then mechanically dried in a hot air oven before being shirred and packaged.
In another known process as disclosed in patent specifications GB 991183, U.S. Pat. No. 3,235,641 and U.S. Pat. No. 3,579,358, the collagen gel is extruded into a salt bath (containing for example ammonium sulphate or sodium chloride) and is then tanned using an alum bath. The wet casing is then mechanically dried.
U.S. Pat. No. 3,930,035 discloses extruding the collagen gel into a coagulating salt bath. The casing is then passed into a first tanning bath comprising aluminium sulphate and sodium citrate. It is then passed into a second tanning bath containing glutaraldehyde.
However, the processing conditions disclosed in these prior specifications aim at producing a collagen casing which is to be air dried prior to packaging and use. They do not address the problem of providing a wet casing of sufficient strength to be used in the wet state.
It is an object of the present invention to mitigate these problems and to provide a casing of adequate mechanical properties for use in the wet state.